Numerous studies have to better understand the morphology and physiology of muscle and the etiology of injury and associated disorders. Interactions between the active force generator, passive force transmission, and the connective tissue are complicated and need to be further investigated. A newly developed technology, the Magnetic Resonance Elastography (MRE), provides great potential for in vivo investigation non- invasively. MRE images the response of tissue to acoustic shear waves to determine the shear modulus as well as the tension in the muscle. The specific aims of this study are: Aim 1: To Develop Practical Methods for Imaging Acoustic Shear Waves in Skeletal Muscle under Varied Loading Conditions: Develop electromechanical drivers and support devices that are designed specifically for applying shear waves to skeletal muscle. Develop a multislice version of the MRE pulse sequence with 3 axes of motion encoding, suitable for imaging shear waves in skeletal muscle over large fields of view. Develop a 3D acquisition sequence with similar capabilities. Evaluate various approaches for reducing acquisition time. Design and fabricate an MRI-compatable muscle loading system. Aim 2: To Develop Image Analysis Methods for MR Elastography of Skeletal Muscle: Develop and test several different approaches for measuring local wavelength in MRE images. Incorporate adjustments in the algorithms to accommodate waveguide phenomena that have been observed in preliminary studies. Develop methods for using MRI- derived muscle volumetric information to estimate regional fiber tension. Aim 3: To Utilize Magnetic Resonance Elastography to Study Normal Muscle In Vivo: The MRE technique will be applied in vivo to provide elastographic images of the muscles in the extremity of volunteers. Basic characteristics of muscle that include the moduli or stiffness of muscles as a function of the tension, the loading rate and the frequency of perturbation will be validated. Uniformity of tension distribution within the muscle will also be examined. Aim 4: To Utilize Magnetic Resonance Elastography to Study Abnormal Muscle In Vivo: The MRE technique will be applied in vivo to provide elastographic images of abnormal muscle, with known disorders to differentiate the physiology of normal and diseased muscle. Successful application of this technique will provide a means for assessing efficacy of various rehabilitation procedures.